User Manual

90
Remarks of Siemens
This section outlines how Siemens interprets the functions and processing functions according
to EN 15232-1:2017.
4.6
1 When cooling the extract air for heat recovery purposes the humidity contained in the air can
condensate. At low temperatures this condensate can freeze at the heat exchanger surface.
Because of this the free cross-section for the air flow through the heat exchanger can be partially
or completely closed off.
Fans with variable speed drives (VSD) react to an increasing resistance at the heat exchanger
with increasing the fan speed in order to still provide the required air flow. This leads to increased
power consumption.
If fans with constant speed are used, then, with the increasing resistance, the air flow on the
extract side of the heat exchanger will be reduced in case of icing. With the power consumption
remaining about the same, an undesirable over-pressure situation in the ventilation system
occurs. This should be avoided.
Not all heat recovery constructions are similarly prone to icing. With rotating heat exchangers this
risk occurs only at very low outside air temperatures. For details on this the manufacturer’s
documentation should be consulted.
This protection function reduces the capacity of the heat recovery system (e.g. via bypass
damper for plate exchangers, diverting valve in a CVS-System). The reduced capacity must be
compensated with the following air heating coil in the air handling unit.
4.7
0 This is often the case in plants where separate (independent) control loops are utilized for the
heat recovery and the pre-heating and heating coils.
1 This is today’s typical solution that utilizes heating/cooling sequences of the temperature control
loop appropriately. By sequencing of the different devices such as heat recovery unit, heating coil
and cooling coil they will be properly interlocked.
4.8
2 Cooling and ventilation with a portion of passive energy (renewable and at no cost can still require
some energy, e.g. electrical energy for supply pumps). With that the portion of active energy (with
costs) can be reduced.
4.10
1 Precondition for dew point control is an air humidifier (air washer) with a humidification efficiency
of at least 95 %, by that practically reaching a fully saturated air condition. By controlling to the
temperature of this saturated air the humidity content is also fixed. The required control
infrastructure for it is relatively small. This solution is only suitable in cases where the air that has
been cooled down to the dew point will be reheated in the room by internal (excessive) heat. If
this is not the case, a direct humidity control should be implemented in air conditioning systems
for efficiency reasons.
2 With spray humidification much lower humidification efficiency than for a dew point humidifier is
sufficient. Therefore a less costly device can be utilized. Important is that this device can be
controlled within a sufficiently large range.